Aims: To quantify the avoidable burden of colorectal cancer in Australia by modifications in lifestyle-related risk factors.
Methods: Data on exposure to lifestyle-related risk factors from seven Australian cohort studies (N=367,772) were harmonised and pooled. The cohorts were linked to the Australian Cancer Database and National Death Index to identify incident cancers and deaths. The strength of the exposure-cancer association was estimated using a proportional hazards model, adjusting for age, sex and the other lifestyle exposures. Exposure prevalence was estimated from the Australian National Health Survey 2011-2012, except for red and processed meat consumption, which was estimated from the 45 and Up cohort study. These estimates were then combined to calculate the Population Attributable Fractions (PAFs) and their 95% confidence intervals (CIs) using an advanced method accounting for competing risk of death.
Results: During the first 5-years follow-up, 7,612 deaths (all causes) and 1,906 incident colorectal cancers were ascertained. Smoking (current or former) explains 8% (CI 3-13%), BMI ≥ 25 kg/m2 8% (CI 1-14%), red or processed meat consumption more than 3 times/week 6% (CI 2-9%), and drinking more than 2 alcoholic drinks/day 4% (CI 1-7%) of the colorectal cancer cases. Having one or more of these risk factors explains altogether 24% (CI 10-36%) of the cases. The contribution of all risk factors was more pronounced in men than in women. The PAF results for physical activity were not significant. Based on projected Australian incidence rates for 2016-2020, the PAF estimate of 24% equates to 22,700 avoidable colorectal cancer cases over 5 years.
Conclusions: These first Australian colorectal cancer PAF estimates based on cohort studies and accounting for competing risk of death show that several modifiable risk factors contribute to the burden of colorectal cancer. Due to its high incidence, these PAF estimates translate into a significant number of avoidable cases.